Chapter 01 Introduction to Construction Materials & Testing

• Materials Engineer - responsible for the selection, specification and quality control of materials
• FACTORS THAT MATERIALS ENGINEER CONSIDER

  ➢ Economic Factors

  ➢ Mechanical properties

  ➢ Nonmechanical properties

  ➢ Production

  ➢ Aesthetic properties
• ECONOMIC - isn’t just affected by the cost of materials
• Factors that should be considered for economic factors are:

  • Availability and cost of the raw materials

  • Manufacturing cost

  • Transportation

  • Placing

  • Maintenance
• Using readily available materials can reduce transportation costs and environmental impact
• In remote areas, the cost of transporting materials may influence the decision to use locally sourced materials.
• Manufacturing cost includes not only the material cost but also installation, maintenance, and life cycle costs
• Balancing quality with cost efficiency is a key decision factor under manufacturing cost.
• Materials that are bulky or heavy may require specialized transport and handling.
• Steel-frame buildings are easier and faster to build than reinforced concrete buildings, because steel can be made in a shop and assembled on site.
• Reinforced concrete buildings require more steps and time on site, such as building forms, placing steel and concrete, and removing forms.
• Precast concrete units are used to avoid some of these problems, especially for bridges.
• When choosing a material for a structure, the total cost over its lifetime should be considered, not just the initial cost of building it.
• The specific response of a material to deformations depends on its properties, the magnitude and type of loads, and the geometry of the material.
• Whether the material fails under the load conditions depends on the failure criterion.
• Static loads are loads that don’t disturb the structure or material through vibrations or shock
• Static loads are sustained loading of the structure over a period.
• Dynamic loads are loads that disturb the material or structures through vibrations and shocks
• Periodic - Harmonic or sinusoidal loads (repeating pattern)
• Random - never repeating loads such as earthquake loads
• Transient - impulse load (applied over short period) such as vibrations caused by winds and trucks
• Periodic

  
• Random

  
• Transient

  
• When a material is subjected to a load or force, it changes its shape or size. This change is called deformation
• Robert Hooke, a scientist, discovered in 1678 that there is a simple mathematical formula that describes how much a material deforms when a force is applied
• The formula says that the deformation depends on the material's properties and its dimensions.
• The effect of the dimensions can be expressed as a ratio to make the formula more general.
• Typical uniaxial stress-strain diagrams for Glass and Chalk

  
• Typical uniaxial stress-strain diagrams for Steel

  
• Typical uniaxial stress-strain diagrams for Aluminum Alloys

  
• Typical uniaxial stress-strain diagrams for Concrete

  
• Typical uniaxial stress-strain diagrams for Soft Rubber

  
• If a material exhibits true elastic behavior, it must have an instantaneous response (deformation) to load, and the material must return to its original shape when the load is removed
• Elastic deformation does not change the arrangement of atoms within the material, but rather it stretches the bonds between atoms. When the load is removed, the atomic bonds return to their original position.
• Young observed that different elastic materials have different proportional constants between stress and strain.
• For a homogeneous, isotropic, and linear elastic material, the proportional constant between normal stress and normal strain of an axially loaded member is the modulus of elasticity or Young’s modulus
• Young’s Modulus of Elasticity – the property of a material to withstand compression or the elongation with respect to its length.
• Young's Modulus of Elasticity is equal to the longitudinal stress divided by the strain.
• In the axial tension test, as the material is elongated, there is a reduction of the cross section in the lateral direction.